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View Full Version : Graceful Switchover with RAC


Mike Donovan
01-18-2012, 02:19 PM
Graceful Switchover can be used with Oracle RAC and works identical to Graceful Switchover with single instance databases. However the following applies:

1. Graceful Switchover can only occur between ONE primary node and the standby server. The instance on the other primary node(s) will be automatically shutdown during graceful switchover. If Graceful Switchover is started on ServerA and ServerC, then ServerA and ServerC will be reversed. The RAC instance on ServerB will be automatically shutdown and will no longer be a part of the configuration until Graceful Switchover is initiated again to bring the configuration back to the original configuration.

2. Graceful Switchover will convert any RAC database to single instance database by setting cluster_database database parameter to FALSE. Upon completion of graceful switchover, this parameter can be set to TRUE again to convert the single instance back into a RAC database.

3. The switch over process may take longer with a RAC and ASM database than with a regular file system database. The reason for this is the extra time taken to extract Oracle files out of ASM.

4. If the standby database uses multiple nodes RAC configuration, all standby instances except for the one that is involved in Graceful Switchover, should be manually shut down prior to proceeding with switchover.

Graceful Switchover with RAC example
With the following configuration:
ServerA RAC instance dbvrac1 (primary)
ServerB RAC instance dbvrac2 (primary)
ServerC Single instance standby database dbvrac (standby)

Graceful Switchover is initiated on both ServerA and ServerC with command:
dbv_oraStartStop switchover dbvrac1

The following will occur:
1. RAC database dbvrac2 on ServerB will be shutdown.
2. RAC database dbvrac1 will be converted to a single instance standby database.
3. Single instance standby database on ServerC will be converted to a single instance primary database with 2 threads:
ServerA Single instance standby database dbvrac1 (standby)
ServerB RAC instance shutdown (standby)
ServerC Single instance primary database dbvrac (primary)

If Graceful Switchover is initiated again to bring it back to the original configuration the following will occur:
1. Single instance standby database dbvrac1 on ServerA will be converted to a single instance primary database with 2 threads.
2. Single instance primary database dbvrac on ServerC will be converted to a single instance standby database with 2 threads:
ServerA Single instance primary database dbvrac1 (primary)
ServerB RAC instance shutdown (primary)
ServerC Single instance standby database dbvrac (standby)

To convert from a single instance primary database back to a RAC database:
1. On ServerA, set database parameter cluster_database=TRUE in database dbvrac1.
2. Restart instance dbvrac1 on ServerA.
3. Start dbvrac2 instance on ServerB.
4. Dbvisit Standby can be initiated again as normal on ServerA and ServerC:
dbvisit dbvrac1

5. On other nodes that were not part of the graceful switchover (in this case ServerB), Dbvisit Standby must be resynchronised with the standby database by running command:
dbvisit -R dbvrac2

The command only needs to run once. After this command, Dbvisit Standby can be run as normal:
dbvisit dbvrac2


Taken from the Dbvisit Standby User Guide version 6.0.09 pages 182-83.